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Karig, Daniel E.

Abstract

Discussion of the Quaternary geology of the Sixmile watershed is logically separated into two
sections: the Sixmile-Willseyville Trough and the upper Sixmile drainage, both of which can be further
divided into sub-units based on geological characteristics. The Sixmile Trough section displays evidence
for 4 glacial advances based on morphologic and/or lithologic criteria. The oldest advance is associated
with the broad U-shaped upper valley slope section and is possibly pre-Illinoian. The probable Illinoian
age of an inner glacial trough is derived from the assumed Sangamon age of a very large interglacial
gorge incised into the floor of that trough. The inner glacial trough is overlain by an array of mid-
Wisconsin (Cherrytree stade) deposits that document a glacial advance that reached into the Sixmile
Trough. An interstadial gorge was cut into the base of the Sangamon gorge, probably following the mid
Wisconsin glaciation but before the Late Wisconsin glaciation, which overrode the entire area and
overprinted most of the earlier glacial features.

The ice front retreat from the Late Wisconsin glacial maximum (Nissouri stade) is best documented in
the Willseyville Trough and upper Sixmile drainage. Well data indicate that the ice front during the Erie
interstade did not retreat far north of the Sixmile-Willseyville trough-upper Sixmile junction, which
would explain the single Late Wisconsin till in the Sixmile Trough. The subsequent Port Bruce readvance
produced the Valley Heads moraines, which are characterized by large outwash plains but few
end moraines or lateral moraines on the interfluves. However, several such moraines and ice margin
channels in the upper Sixmile drainage outline the shape of the Port Bruce ice front there. Ice stagnation
following the Port Bruce advance led to extensive kame and kettle terrains behind the ice front maxima
and to a small lake trapped between the Willseyville Trough and Upper Sixmile valley. A large delta fed
sediment from the upper Sixmile basin into this lake. Till interbedded with the deltaic foresets
demonstrate that active ice closed this lake at times. The lake drained, probably catastrophically, through
a large channel, here termed the Willseyville channel, now marked by a series of wetlands separated by
alluvial fans. A minor “Brooktondale” re-advance is marked by a till overlying the delta and by a lateral
moraine that can followed from the east side of Inlet Valley across the interfluves into the Sixmile Creek
valley and onto its northern slope. The Brooktondale re-advance is here correlated with the Hatfield
event in New England and the Little Falls re-advance in the Mohawk valley, at about 13.25 14C ka BP.
An unusual channel, located at the front of this ice advance near the Brooktondale delta, changes its
downstream direction 180 ° from southerly to northerly and cuts across and downward through the delta.
It is most easily explained as an englacial to subglacial channel that drained NW under the ice of the
Sixmile Trough. This would require subglacial drainage down the Sixmile Trough and northward along
the Cayuga Trough into the Mohawk valley, which was ice-free at this time. Sub-glacial drainage at this
time would explain the lack of lacustrine sediments in the southeast section of the Sixmile Trough.
Subglacial drainage was apparently soon blocked and a proglacial lake formed in the Sixmile and
Cayuga troughs because a deltaic or lake marginal, coarsening upward sequence of fine sand to gravel
overlies the till in the northwest section of the Sixmile Trough. A planar cap of coarse gravel and cobble
descends northwesterly along the Trough from an elevation of approximately 780’ at the 30’ dam to 600’
at Van Natta’s dam, indicating a rapid decreasing surface elevation of this proglacial lake. This decrease
in elevation is attributed to the retreating Laurentide ice front, which is recorded by recessional moraines
north of Ithaca.